Recent years have seen an explosion of interest in gourmet coffee products and the interest has not been limited to the purchase of coffee-based beverages from vendors who prepare the beverage on premise and purvey it to consumers over the counter. Similarly, the interest has not been limited to gourmet blends, coffee that may be purchased already ground, and then brewed in the home. Many consumers desire the ultimate in freshness and flavor and have taken to roasting their own beans and then grinding them shortly before the coffee brewing process is initiated.
As a consequence, an increasing market for coffee roasting apparatus that may be used in the home has sprung up. A variety of coffee roasting apparatus have been devised to meet this market. One example of such a coffee roasting apparatus is illustrated in U.S. Pat. No. 5,564,331 issued Oct. 15, 1996 to Song, the entire disclosure of which is herein incorporated by reference. The apparatus works well for its intent and purpose, but further improvement is required to meet the increasingly demanding tastes of coffee beverage consumers.
Coffee roasting is a two-step process. The outside of a bean is covered with a husk which also follows a fold into the center of the bean. As it is roasted, the coffee bean expands and literally "pops" to shed the outer husk. If the bean is properly roasted, the center of the bean further expands and allows some of the internal husk to break free of the bean. Removal of the husk considerably improves the flavor of the coffee.
Desirably, coffee beans are roasted in a heated air stream and there is a delicate balance of temperature and air flow required to properly roast the bean. Optimal roasting allows convective heat from the air stream to easily penetrate the husk and cause the internal mass of the bean to quickly rise to a desired temperature. This causes moisture and oil within the bean to vaporize and expand to apply pressure to the husk, resulting in the popping of the bean. The mass of the bean expands and the husk is freed from the bean.
If a bean is roasted at too low of a temperature, the moisture build-up is sufficiently slowed as to allow the vapor to escape without building up sufficient pressure to pop the bean. When this occurs, the bean will be of smaller size than if proper roasting occurs. Some of the husk on the exterior of the bean may remain and most of the husk on the interior of the bean will likewise remain in place. On the other hand, if a bean is roasted at too high of a temperature, the bean will be burned, i.e., overly caramelized, and taste will suffer. In some cases, high temperature roasting will result in a burning of the husk. As the husk serves as a moisture barrier to allow pressure to build up during roasting, the burning of the husk destroys the moisture barrier and allows the moisture to escape without building up sufficient pressure to pop the bean.
The second stage of roasting occurs once the bean pops. Here, the heating of the oil within the bean results in chemical changes to roast the bean to the taste of a particular consumer. In many instances, continued roasting of the bean after popping causes a further expansion of the bean.
To achieve optimum roasting, it is necessary that the beans be uniformly heated. If the heating is not uniform, some of the beans may pop early in the roasting process and others, not at all. Consequently, uniform flavor cannot be obtained.
Similarly, it is necessary that roasting temperature be properly controlled to assure maximum husk removal, as well as proper flavor development which cannot occur if the roasting temperature is either too low or too high.
Heretofore, coffee bean roasters intended for home use have generally subjected the beans to a heated air stream for a period of time selected by the consumer who is operating the roaster. This does not provide adequate temperature control because of many variables involved.
Specifically, a small quantity of beans to be roasted will attain a desired roasting temperature in a lesser amount of time than a larger quantity of beans with the result that the roasts of the two quantities will be quite different.
Secondly, in a typical home coffee bean roaster, wherein a heated air stream is passed through beans in a vessel, a greater quantity of beans will impede air flow through the beans more than if a lesser quantity of beans were present. As a consequence of the impeded air flow, the residence time of the air in the heating instrumentality will increase with the result that the air stream passing through the beans will be of a higher temperature when the quantity of beans is large as compared to when it is small.
Most home coffee bean roasters also include some sort of means for capturing the separated husks as they separate from the body of the bean during the roasting process. Obviously, more husks will separate when a larger quantity of beans are present, and since the separating process typically employs a filter, such as a fine mesh screen, to capture the husks, the build-up of husks on the screen will be greater for a large quantity of beans than for a smaller quantity. This husk build-up will also impede air flow through the beans, with the consequence that the beans will be subjected to a higher temperature air stream.
Another significant factor is line voltage. Typical home coffee bean roasters are electrically operated, i.e., the heating instrumentality is an electrical resistance heater. Due to differences in service location, electrical loading of the home electrical system as when other electrical appliances are operating or turned off, or simply due to fluctuations in line voltage as a result of transitory conditions within an electrical distribution system for a wide area, line voltage will not untypically vary from 105 volts up to 130 volts or more on a line intended to provide a 120 volt alternating current. When low voltage conditions occur, the heat up of the electrical heating element used to heat the air stream will be slower than would be the case under normal voltage conditions which, in turn, would be slower than would be the case for high voltage situations. As a consequence, line voltage fluctuations have a significant effect on the temperature of the air stream applied to the beans in the roaster and, of course, on the outcome of the roasting process. Low voltage conditions can thus result in an under-roast, including inadequate hull popping, while high voltage conditions can result in over-roasting, including burning or over-caramelizing of the beans to be roasted.
The present invention is directed to overcoming one or more of the above problems.